Just to chime in that I do taxes and I'm a mom, and the amount on our Form 6419 also seemed incorrect: only half of the amount reported in the CTC portal.  But apparently even for married filing jointly they are sending two separate letters to spouses. Rather than the letters being duplicates, you're supposed to add the amounts together. There may be actual errors but it may be worth asking your client if they are adding the two together or assuming they were duplicates.